Method for improving the regulatory behavior of motor vehicle regulatory systems

ABSTRACT

The invention relates to a method for improving the control behavior of motor vehicle control systems such as ABS, ESP, etc. comprising electrically driven hydraulic pumps, inlet and outlet valves and low-pressure accumulators, wherein the low-pressure accumulators accommodate, at least in part, pressure fluid that is discharged from wheel brakes in a control operation, wherein the hydraulic pumps are used to return the pressure fluid into a master cylinder, in particular tandem master cylinder, wherein the delivery behavior of the hydraulic pumps is controlled in dependence on pressure values, and wherein the actuation of the hydraulic pumps takes place in conformity with demand, i.e. by evaluating slip variation, wherein in a pressure increase phase, the pressure fluid is intermediately stored in the low-pressure accumulators and there is no return delivery of the pressure fluid into the master cylinder until either a pressure increase phase or pressure buildup commences, or a critical filling level of the low-pressure accumulator necessitates actuation of the hydraulic pumps for safety reasons, with the result of balancing the volume flow demand and the delivery volume flow and thus achieving a reduction of vibrations of the brake pedal. Further, the invention relates to a computer program product defining an algorithm that comprises a method for improving the control behavior of motor vehicle control systems.

TECHNICAL FIELD

The present invention relates to a method for improving the controlbehavior of motor vehicle control systems such as ABS, ESP, etc.comprising electrically driven hydraulic pumps, inlet and outlet valvesand low-pressure accumulators, wherein the low-pressure accumulatorsaccommodate, at least in part, pressure fluid that is discharged fromwheel brakes in a control operation, wherein the hydraulic pumps areused to return the pressure fluid into a master cylinder, in particulartandem master cylinder, wherein the delivery behavior of the hydraulicpumps is controlled in dependence on pressure values, and wherein theactuation of the hydraulic pumps takes place in conformity with demand,i.e. by evaluating slip variation, and a computer program product.

BACKGROUND OF THE INVENTION

DE 19632311 A1 discloses a control strategy for the actuation of a pumpbased on a pressure volume model, wherein the pump actuation isperformed under the aspect of giving priority to the evacuation of thelow-pressure accumulators. In this arrangement, the delivery rate of thehydraulic pump is dimensioned such that the time period between twosuccessive phases of brake pressure reduction is sufficient for thecomplete evacuation of the low-pressure accumulators.

The prior-art pump actuation impairs the pedal comfort because thedelivery volume flow is not in balance with the volume flow required(pressure increase pulses). Especially in situations where there is norisk of filling the low-pressure accumulators or when the pilot pressureexceeds the locking pressure level only slightly, a conventional pumpactuation of this type is uncomfortable or even impairs the controlquality (e.g. on a low coefficient of friction) because the pilotpressure is significantly modified due to an unbalanced return delivery.This change of the pilot pressure causes the known vibrating of thebrake pedal during ABS intervention. The vibrating is the result of thebrake pedal displacing in the direction of the vehicle bottom whenpressure is built up because volume is consumed in a control operation.Hence, the brake pedal is moved in an opposite direction, towards thedriver's foot, superimposed by the delivery pump's activity.

BRIEF SUMMARY OF THE INVENTION

In view of the above, an object of the invention is to provide a methodthat significantly reduces any unwanted movement (vibrating) of thebrake pedal during an ABS intervention by way of a purposeful pumpactuation so that the pedal comfort is enhanced and the control qualityimproved, in particular in low coefficients-of-friction situations.

This object is achieved according to the invention by means of thedescribed method for improving the control behavior of motor vehiclecontrol systems.

It is preferred according to the method of the invention that thecritical filling level of the low-pressure accumulator is fixed inresponse to vehicle-related conditions such as the variation of slip,wheel acceleration, pilot pressure, locking pressure level, etc. In aparticularly preferred fashion, the critical filling level of thelow-pressure accumulator is fixed by means of characteristic curves.

Further, it is preferred that in a pressure increase phase the pressurefluid is returned by means of the hydraulic pumps from the low-pressureaccumulators into the master cylinder in such a fashion that the volumeflow demand of the wheel brake is provided to the greatest possibleextent by the delivery volume flow of the hydraulic pump so that anyunwanted pedal movement due to volume flow differences is minimized.

It is also preferred that the volume flow demand of the wheel brake isstored in the form of volume characteristic curves.

The hydraulic pump is preferably actuated in response to the volumecharacteristic curves.

The invention also relates to a computer program product comprising themethod of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic design of a brake circuit of a vehicle with ABScontrol.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Only one of the usually two brake circuits is shown in FIG. 1 for thesake of clarity. Two brake circuits I, II are connected to a tandemmaster cylinder THZ. The wheel brake B1 of the left front wheel VL andthe wheel brake B2 of the right rear wheel HR are connected to the brakecircuit I in the embodiment shown. It is of course also feasible toallot the brake circuits to the front axle and the rear axle. Inletvalves EV1, EV2 being configured as normally open (NO=open in theirde-energized state) valves are arranged in the pressure fluid lines DLbetween the tandem master cylinder THZ and the wheel brakes B1, B2. Saidinlet valves EV1, EV2 can be closed in an ABS control intervention totemporarily prevent further pressure buildup in the wheel brake by meansof the tandem master cylinder THZ. When pressure reduction is necessaryduring ABS control, the excessive pressure fluid can be dischargedthrough outlet valves AV1, AV2. Said outlet valves AV1, AV2 areconfigured as normally closed valves (NC=closed in their de-energizedstate). The excessive pressure fluid is intermediately stored in alow-pressure accumulator NDS and returned by a hydraulic pump HP drivenby a motor M in front of the inlet valves EV1, EV2. A return delivery ofthe pressure fluid takes place only when a pressure increase phase orpressure buildup commences through the inlet valve or a critical fillinglevel of the low-pressure accumulator NDS necessitates actuation of thehydraulic pump for safety reasons. The pressure buildup being expectedor the increase gradients of the wheel brakes B1, B2 being expected iscalculated by means of a pressure sensor (e.g. in the tandem mastercylinder) or by creating a pressure model. This function is alreadyutilized in order to determine the wheel pressure reproduced in a model,and the pressure increase is likewise stored in the form of volumecharacteristic curves. The volume flow of the hydraulic pump HP islikewise known or can be assessed in the different actuations. Now therequired pump actuation is calculated from the stored volumecharacteristic curve of the wheel brakes B1, B2.

The actuation is executed in consideration of the drifting of thehydraulic pump HP when said produces a still sufficient amount of volumeflow. Drifting of the hydraulic pump HP is considered at a decreasingrate in order to ensure return delivery at a high pedal counterpressure(by way of the driver's foot). At low pilot pressures, drifting becomesa problem when actuation is initiated directly before a pressurereduction phase. This is especially the case when slip conditionsprevail at several wheels. In this situation, a pressure reductionannouncing itself (inlet valves closed) is detected by evaluation of thewheel acceleration and/or the slip variations (ACCF response, pausedoubling), and pump actuation can be suppressed so that drifting doesnot continue until the reduction phase.

Also, the reduced actuation of the hydraulic pump HP or the suppressionof the actuation has a decisive advantage in terms of control technologyon low coefficients of friction, in connection with pilot pressuresbeing only slightly in excess of the locking pressure level. In thissituation, a rise of the pilot pressure because of the return deliveryis avoided as no pressure fluid is conducted in front of the inletvalves, which would have as a result a tandem master cylinder pressureincrease in this situation that is significant in relation to theprevailing locking pressure level due to the delivery ‘against thedriver's pilot pressure’. Hence, the calculation of the buildup, whichhas the previous increase phase as a basis for the calculation, is notdisturbed, and there is no shift from very long increase phases to veryshort increase phases. This enhances pedal comfort as well as thehomogeneity of deceleration.

Partial filling of the low-pressure accumulator NDS can be accepted fora long period of time because no abrupt change from a low coefficient offriction to a considerably lower frictional value is allowed to occur.Only when the wheel pressures reproduced in a model or measured exhibita value of almost zero, without a corresponding re-acceleration of thewheels being detected, will this comfort-oriented pump actuation be leftand the known actuation activated.

1. Method for improving the control behavior of motor vehicle controlcomprising electrically driven hydraulic pumps, inlet and outlet valvesand low-pressure accumulators, wherein the low-pressure accumulatorsaccommodate, at least in part, pressure fluid that is discharged fromwheel brakes in a control operation, wherein the hydraulic pumps areused to return the pressure fluid into a master cylinder, in particulartandem master cylinder, wherein the delivery behavior of the hydraulicpumps is controlled in dependence on pressure values, and wherein theactuation of the hydraulic pumps takes place in conformity with demand,wherein in a pressure decrease phase, the pressure fluid isintermediately stored in the low-pressure accumulators and there is noreturn delivery of the pressure fluid into the master cylinder untileither a pressure increase phase commences, or a critical filling levelof the low-pressure accumulator necessitates actuation of the hydraulicpumps for safety reasons, with the result of balancing the volume flowdemand and the delivery volume flow and thus achieving a reduction ofvibrations of the brake pedal.
 2. Method as claimed in claim 1, whereina measured pilot pressure of a brake pedal is used as a pressure value.3. Method as claimed in claim 1, wherein the pressure value is apressure value calculated by producing a model from values acquired onthe basis of the valve actuation, the control variation etc.
 4. Methodas claimed in claim 1, wherein the critical filling level of thelow-pressure accumulator is fixed in response to vehicle-relatedconditions such as the variation of slip, wheel acceleration, pilotpressure, locking pressure level, etc., in particular by means ofcharacteristic curves.
 5. Method as claimed in claim 1, wherein in apressure increase phase, the pressure fluid is returned by means of thehydraulic pumps from the low-pressure accumulators into the mastercylinder in such a fashion that the volume flow demand of the wheelbrake is provided to the greatest possible extent by the delivery volumeflow of the hydraulic pump so that pedal movements due to volume flowdifferences are greatly minimized.
 6. Method as claimed in claim 1,wherein the volume flow demand of the wheel brake is stored in the formof volume characteristic curves.
 7. Method as claimed in claim 6,wherein the hydraulic pump is actuated in response to the volumecharacteristic curves.
 8. Computer program product, wherein said productdefines an algorithm comprising a method as claimed in claim
 1. 9.Method for controlling a motor vehicle control system comprising atleast one hydraulic pump, inlet and outlet valves and at least onelow-pressure accumulator, wherein the low-pressure accumulatoraccommodates, at least in part, pressure fluid that is discharged fromone or more wheel brakes in a control operation, wherein the at leastone hydraulic pump is used to return the pressure fluid into a mastercylinder, the method comprising: controlling the delivery behavior ofthe at least one hydraulic pump in dependence on pressure values; andactuating the at least one hydraulic pump in conformity with demand,wherein in a pressure decrease phase, the pressure fluid isintermediately stored in the at least one low-pressure accumulator andthe at least one hydraulic pump is deactivated until either a pressureincrease phase commences or a critical filling level of the low-pressureaccumulator is reached.
 10. Method as claimed in claim 9, wherein ameasured pilot pressure of a brake pedal is used as a pressure value.11. Method as claimed in claim 9, wherein the pressure value is apressure value calculated by producing a model from values acquired onthe basis of the valve actuation and the control variation.
 12. Methodas claimed in claim 9, wherein the critical filling level of thelow-pressure accumulator is fixed in response to vehicle-relatedconditions such as the variation of slip, wheel acceleration, pilotpressure, and locking pressure level.
 13. Method as claimed in claim 12,wherein the critical filling level of the low-pressure accumulator isfixed by means of characteristic curves.
 14. Method as claimed in claim9, wherein in a pressure increase phase, the pressure fluid is returnedby means of the at least one hydraulic pump from the at least onelow-pressure accumulator into the master cylinder in such a fashion thata volume flow demand of the wheel brake is provided to the greatestpossible extent by the delivery volume flow of the hydraulic pump sothat pedal movements due to volume flow differences are greatlyminimized.
 15. Method as claimed in claim 14, wherein the volume flowdemand of the wheel brake is stored in the form of volume characteristiccurves.
 16. Method as claimed in claim 15, wherein the hydraulic pump isactuated in response to the volume characteristic curves.
 17. Computerprogram product, wherein said product defines an algorithm comprising amethod as claimed in claim 9.